ef|fi|ca|cy

ef|fi|ca|cy «EHF uh kuh see», noun, plural -cies.

the power to produce the effect wanted; effectiveness: »

The efficacy of aspirin in relieving headaches is well known.

╂[< Latin efficācia < efficāx, -ācis efficacious < efficere accomplish; see etym. under efficient (Cf. ↑efficient)]